Method for high density data storage and imaging

ABSTRACT

An approach is presented for designing a polymeric layer for nanometer scale thermo-mechanical storage devices. Cross-linked polyimide oligomers are used as the recording layers in atomic force data storage device, giving significantly improved performance when compared to previously reported cross-linked and linear polymers. The cross-linking of the polyimide oligomers may be tuned to match thermal and force parameters required in read-write-erase cycles. Additionally, the cross-linked polyimide oligomers are suitable for use in nano-scale imaging.

RELATED APPLICATIONS

The present application is a continuation-in-part of and claims priorityof copending application Ser. No. 11/358,774 filed on Feb. 21, 2006.

FIELD OF THE INVENTION

The present invention relates to the field of high density data storageand imaging and more specifically to a data storage and image medium, adata storage and imaging system, and a data storage and imaging method.

BACKGROUND OF THE INVENTION

Current data storage and imaging methodologies operate in the micronregime. In an effort to store ever more information in ever smallerspaces, data storage density has been increasing. In an effort to reducepower consumption and increase the speed of operation of integratedcircuits, the lithography used to fabricate integrated circuits ispressed toward smaller dimensions and more dense imaging. As datastorage size increases and density increases and integrated circuitdensities increase, there is a developing need for data storage andimaging methodologies that operate in the nanometer regime.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a method, comprising: heatinga probe to at least 100° C.; pushing the heated probe into across-linked resin layer of polyimide oligomers; and removing the probefrom the resin layer, resulting in formation of a deformed region in theresin layer.

A second aspect of the present invention is the first aspect, whereinthe polyimide oligomers have the structure:

wherein R′ is selected from the group consisting of

wherein R″ is selected from the group consisting of

wherein n is an integer from about 5 to about 50.

A third aspect of the present invention is the second aspect wherein thelayer of polyimide oligomers includes a reactive diluent, the reactivediluent selected from the group consisting of:

where R₁, R₂ and R₃ are each independently selected from the groupconsisting of hydrogen, alkyl groups, aryl groups, cycloalkyl groups,alkoxy groups, aryloxy groups, alkylamino groups, arylamino groups,alkylarylamino groups, arylthio, alkylthio groups and

wherein the polyimide oligomers are cross-linked by reactive diluentgroups derived from the reactive diluent during the curing.

A fourth aspect of the present invention is the third aspect, wherein aglass transition temperature of the resin layer with the reactivediluent groups is within about 50° C. of a glass transition temperatureof an otherwise identical resin layer formed without the reactivediluent groups.

A fifth aspect of the present invention is the first aspect wherein thepolyimide oligomers have the structure:

E-R¹A₁-A₂-A₃- . . . -A_(N)R²-R¹-E;

wherein E is

wherein each of A₁, A₂, A₃ . . . A_(N) is independently selected fromthe group consisting of:

wherein R¹ is selected from the group consisting of

wherein R² is selected from the group consisting of

wherein R³ is

wherein N is an integer greater than or equal to 2;wherein at least one of A₁, A₂, A₃ . . . A_(N) is

wherein at least one of A₁, A₂, A₃ . . . A_(N) is

A sixth aspect of the present invention is the first aspect whereinafter the curing, the resin layer is cross-linked by the reactiveendgroups of the polyimide oligomers.

A seventh aspect of the present invention is the first aspect whereinthe polyimide oligomers include reactive pendent groups attached alongbackbones of the polyimide oligomers and after the curing, the resinlayer is cross-linked by the reactive pendent groups.

A eighth aspect of the present invention is the first aspect, wherein aglass transition temperature of the resin layer is less than about 250°C.

A ninth aspect of the present invention is the first aspect, wherein amodulus of the resin layer above a glass transition temperature of theresin layer is between about 1.5 and about 3.0 decades lower than amodulus of the resin layer below the glass transition temperature of theresin layer.

A tenth aspect of the present invention is the first aspect, wherein theresin layer is thermally and oxidatively stable to at least 400° C.

An eleventh aspect of the present invention is the first aspect, furtherincluding: removing the resin layer in the deformed region to form anexposed region of a substrate and a region of substrate protected by theresin layer; and modifying at least a portion of the exposed region ofsubstrate.

A twelfth aspect of the present invention is the first aspect, furtherincluding: dragging the probe in a direction parallel to a top surfaceof the resin layer while heating and pushing the probe, resulting information of a trough in the resin layer.

A thirteenth aspect of the present invention is the first aspect,wherein the cross-linked resin layer has a thickness between about 10 nmand about 500 nm and a thickness variation of less than about 1.0 nmacross the cross-linked resin layer.

A fourteenth aspect of the present invention is a method, comprising:heating a probe to at least 100° C.; pushing the heated probe into across-linked resin layer of polyimide oligomers; and removing the probefrom the resin layer, resulting in formation of a deformed region in theresin layer.

A fifteenth aspect of the present invention is a data storage device,comprising: a recording medium comprising a resin layer overlying asubstrate, in which topographical states of the resin layer representdata, the resin layer comprising cross-linked polyimide oligomers; and aread-write head having one or more thermo-mechanical probes, each of thethermo-mechanical probes including a resistive region locally heating atip of the thermo-mechanical probe in response to electrical currentbeing applied to the thermo-mechanical probe; and a scanning system forscanning the read-write head across a surface of the recording medium.

BRIEF DESCRIPTION OF DRAWINGS

The features of the invention are set forth in the appended claims. Theinvention itself, however, will be best understood by reference to thefollowing detailed description of illustrative embodiments when read inconjunction with the accompanying drawings, wherein:

FIGS. 1A through 1C illustrate the structure and operation of a tipassembly for a data storage device including the data storage mediumaccording to the embodiments of the present invention;

FIG. 2 is an isometric view of a local probe storage array includingdata storage medium according to the embodiments of the presentinvention;

FIGS. 3A through 3D are cross-section views illustrating formation of apattern in a substrate according to one embodiment of the presentinvention;

FIGS. 4A through 4E are cross-section views illustrating formation of apattern in a substrate according to another embodiment of the presentinvention;

FIGS. 5A through 5E are cross-section views illustrating formation of apattern in a layer on a substrate according to an embodiment of thepresent invention;

FIG. 6 is a diagram illustrating cross-linking of a polyimide resin witha reactive diluent according to embodiments of the present invention;

FIG. 7 is thermo-gravimetric analysis plotting percentage of weightremaining and temperature versus time of a polyimide resin according toan embodiment of the present invention compared to polystyrene resins;

FIG. 8 is a plot of modulus versus temperature of polyimide resinsaccording to embodiments of the present invention;

FIGS. 9A through 9D are SEM photomicrographs of tips of various tipassemblies; and

FIG. 10 is an AFM scan-line cross-section showing data bits written in astorage medium according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

For the purpose of describing the present invention, on a scale of 0-100units, a decade is 10 units. On a scale of 0-1000, a decade is 100units. Therefore a decade of a range is defined as one-tenth of therange of units from 0 units to 10^(n) units, wherein n is a wholepositive integer equal to or greater than 0.

FIGS. 1A through 1C illustrate the structure and operation of a tipassembly 100 for a data storage device including the data storage mediumaccording to the embodiments of the present invention. In FIG. 1A, probetip assembly 100 includes a U-shaped cantilever 105 having flexiblemembers 105A and 105B connected to a support structure 110. Flexing ofmembers 105A and 105B provides for substantial pivotal motion ofcantilever 105 about a pivot axis 115. Cantilever 105 includes a tip 120fixed to a heater 125 connected between flexing members 105A and 105B.Flexing members 105A and 105B and heater 125 are electrically conductiveand connected to wires (not shown) in support structure 110. In oneexample, flexing members 105A and 105B and tip 120 are formed ofhighly-doped silicon and have a low electrical resistance, and heater125 is formed of lightly doped silicon having a high electricalresistance sufficient to heat tip 120, in one example, between about100° C. and about 400° C. when current is passed through heater 125. Theelectrical resistance of heater 125 is a function of temperature.

Also illustrated in FIG. 1A is a storage medium (or a recording medium)130 comprising a substrate 130A, and a cured polyimide resin layer 130B.In one example, substrate 130A comprises silicon. Cured polyimide resinlayer 130B may be formed by solution coating, spin coating, dip coatingor meniscus coating uncured polyimide resin formulations and performinga curing operation on the resultant coating. In one example, curedpolyimide resin layer 130B has a thickness between about 10 nm and about500 nm and a variation in thickness of less than about 1.0 nm across thecured polyimide resin layer. The composition of cured polyimide resinlayer 130B is described infra. An optional penetration stop layer 130Cis shown between cured polyimide resin layer 130B and substrate 130A.Penetration stop layer 130C limits the depth of penetration of tip 120into cured polyimide resin layer 130B.

Turning to the operation of tip assembly 100, in FIG. 1A, an indentation135 is formed in cured polyimide resin layer 130B by heating tip 120 toa writing temperature T_(W) by passing a current through cantilever 105and pressing tip 120 into cured polyimide resin layer 130B. Heating tip120 allows the tip to penetrate the cured polyimide resin layer 130Bforming indentation 135, which remains after the tip is removed. In oneexample, the cured polyimide resin layer 130B is heated to above 200° C.by heated tip 120 to form indentation 135. As indentations 135 areformed, a ring 135A of cured polyimide polymer is formed around theindentation. Indentation 135 represents a data bit value of “1”, a databit value of “0” being represented by an absence of an indentation.

FIGS. 1B and 1C illustrate reading the bit value. In FIGS. 1B and 1C,tip assembly 100 is scanned across a portion of cured polyimide resinlayer 130B. When tip 120 is over a region of cured polyimide resin layer130B not containing an indentation, heater 125 is a distance D1 from thesurface of the cured polyimide resin layer (see FIG. 1B). When tip 120is over a region of cured polyimide resin layer 130B containing anindentation, heater 125 is a distance D2 from the surface of the curedpolyimide resin layer (see FIG. 1C) because the tip “falls” into theindentation. D1 is greater than D2. If heater 125 is at a temperatureT_(R) (read temperature), which is lower than T_(W) (write temperature),there is more heat loss to substrate 130A when tip 120 is in anindentation than when the tip is not. This can be measured as a changein resistance of the heater at constant current, thus “reading” the databit value. It is advantageous to use a separate heater for reading whichis mechanically coupled to the tip but thermally isolated from the tip.A typical embodiment is disclosed in Patent Application EP 05405018.2,13 Jan. 2005.

“Erasing” (not shown) is accomplished by positioning tip 120 in closeproximity to indentation 135, heating the tip to a temperature T_(E)(erase temperature) and applying a loading force similar to writing,which causes the previously written indent to relax to a flat statewhereas a new indent is written slightly displaced with respect to theerased indent. The cycle is repeated as needed for erasing a stream ofbits whereby an indent always remains at the end of the erase track.T_(E) is typically greater than T_(W). The erase pitch is typically onthe order of the rim radius. In one example, the cured polyimide resinlayer 130B is heated to above about 200° C. by heated tip 120, and theerase pitch is 10 nm to eliminate indentation 135.

FIG. 2 is an isometric view of a local probe storage array 140 includingdata storage medium according to the embodiments of the presentinvention. In FIG. 2, local probe storage array 140 includes substrate145 having a cured polyimide resin layer 150 (similar to cured polyimideresin layer 130B of FIGS. 1A, 1B and 1C), which acts as thedata-recording layer. An optional tip penetration stop layer may beformed between cured polyimide resin layer 150 and substrate 145. In oneexample, substrate 145 comprises silicon. Cured polyimide resin layer150 may be formed by solution coating, spin coating, dip coating ormeniscus coating uncured polyimide resin formulations and performing acuring operation on the resultant coating. In one example, curedpolyimide resin layer 150 has a thickness between about 10 nm and about500 nm and a variation in thickness across a writeable region of curedpolyimide resin layer 150 of less than about 1.0 nm across the curedpolyimide resin layer. The composition of cured polyimide resin layer150 is described infra. Positioned over cured polyimide resin layer 150is a probe assembly 155 including an array of probe tip assemblies 100(described supra). Probe assembly 155 may be moved in the X, Y and Zdirections relative to substrate 145 and cured polyimide resin layer 150by any number of devices as is known in the art. Switching arrays 160Aand 160B are connected to respective rows (X-direction) and columns(Y-direction) of probe tip assemblies 100 in order to allow addressingof individual probe tip assemblies. Switching arrays 160A and 160B areconnected to a controller 165 which includes a write control circuit forindependently writing data bits with each probe tip assembly 100, a readcontrol circuit for independently reading data bits with each probe tipassembly 100, an erase control circuit for independently erasing databits with each probe tip assembly 100, a heat control circuit forindependently controlling each heater of each of the probe tip assembles100, and X, Y and Z control circuits for controlling the X, Y and Zmovement of probe assembly 155. The Z control circuit controls a contactmechanism (not shown) for contacting the cured polyimide resin layer 150with the tips of the array of probe tip assemblies 100.

During a write operation, probe assembly 155 is brought into proximityto cured polyimide resin layer 150 and probe tip assemblies 100 arescanned relative to the cured polyimide resin layer. Local indentations135 are formed as described supra. Each of the probe tip assemblies 100writes only in a corresponding region 170 of cured polyimide resin layer150. This reduces the amount of travel and thus time required forwriting data.

During a read operation, probe assembly 155 is brought into proximity tocured polyimide resin layer 150 and probe tip assemblies 100 are scannedrelative to the cured polyimide resin layer. Local indentations 135 aredetected as described supra. Each of the probe tip assemblies 100 readsonly in a corresponding region 170 of cured polyimide resin layer 150.This reduces the amount of travel and thus the time required for readingdata.

During an erase operation, probe assembly 155 is brought into proximityto cured polyimide resin layer 150, and probe tip assemblies 100 arescanned relative to the cured polyimide resin layer. Local indentations135 are erased as described supra. Each of the probe tip assemblies 100reads only in a corresponding region 170 of cured polyimide resin layer150. This reduces the amount of travel and thus time required forerasing data.

Additional details relating to data storage devices described supra maybe found in the articles “The Millipede—More than one thousand tips forfuture AFM data storage,” P. Vettiger et al., IBM Journal of Researchand Development. Vol. 44 No. 3, May 2000 and “TheMillipede—Nanotechnology Entering Data Storage,” P. Vettiger et al.,IEEE Transaction on Nanotechnology, Vol. 1, No, 1, March 2002. See alsoU.S. patent Publication 2005/0047307, Published Mar. 3, 2005 to Frommeret al. and U.S. patent Publication 2005/0050258, Published Mar. 3, 2005to Frommer et al., both of which are hereby included by reference inthere entireties.

FIGS. 3A through 3D are cross-section views illustrating formation of apattern in a substrate according to one embodiment of the presentinvention. In FIG. 3A, formed on a substrate 200 is a cured polyimideresin layer 205 (similar to cured polyimide resin layer 130B of FIGS.1A, 1B and IC and cured polyimide resin layer 150 of FIG. 2) which willbe an imaging layer. Cured polyimide resin layer 205 may be formed byapplying (by solution coating, spin coating, dip coating or meniscuscoating) a layer of uncured polyimide oligomers (including reactive endcapping agents and optional reactive diluents or reactive backbonelinking agents as described infra) and then heating the substrate anduncured polyimide oligomers to a curing temperature causingcross-linking of the polyimide oligomers into a polyimide resin.

In FIG. 3B, a heated probe tip 210 is pushed down (perpendicular to atop surface 215 of substrate 200) into cured polyimide resin layer 205and then dragged parallel to top surface 215 of substrate 200 thusexposing a region of substrate 200.

In FIG. 3C, a trench 220 is etched into substrate 200 wherever thesubstrate is not protected by cured polyimide resin layer 205. In FIG.3D, cured polyimide resin layer 205 (see FIG. 3C) is removed.

FIGS. 4A through 4E are cross-section views illustrating formation of apattern in a substrate according to another embodiment of the presentinvention. FIGS. 4A are 4B are similar to FIGS. 3A and 3B except in FIG.4B, heated probe 210 is not pressed completely through cured polyimideresin layer 205 forming a cured polyimide resin thinned region 225 incured polyimide resin layer 205. In FIG. 4C, cured polyimide resinthinned region 225 (see FIG. 4B) is removed exposing top surface 215 ofsubstrate 200 and also producing a thinned cured polyimide resin layer205A. In one example, the removal of cured polyimide resin thinnedregion 225 is done by reactive plasma. In one example, the removal ofcured polyimide resin thinned region 225 is done by controlled exposureto a liquid or a vapor.

In FIG. 4D, trench 220 is etched into substrate 200 wherever thesubstrate is not protected by thinned cured polyimide resin layer 205A.In FIG. 4E, thinned cured polyimide resin layer 205A (see FIG. 4D) isremoved.

FIGS. 5A through 5E are cross-section views illustrating formation of apattern in a layer on a substrate according to an embodiment of thepresent invention. FIGS. 5A and 5B are similar to FIGS. 4A and 4B excepta hard mask layer 230 is formed between substrate 200 and curedpolyimide resin layer 205. In FIG. 5C, cured polyimide resin thinnedregion 225 (see FIG. 5B) is removed exposing a top surface 235 of hardmask layer 225 and also producing a thinned cured polyimide resin layer205A.

In FIG. 5D, trench 240 is etched into hardmask layer 225 wherever thesubstrate is not protected by thinned cured polyimide resin layer 205A.In FIG. 5E, thinned cured polyimide resin layer 205A (see FIG. 5D) isremoved. Hardmask layer 230 may be used to etch substrate 200 or toblock diffusion and ion implantation or as a mandrel for deposition ofother coatings including conformal coatings.

The methodologies illustrated in FIGS. 3A through 3D, 4A through 4E and5A through 5E may advantageously be applied to fabrication of integratedcircuits and other semiconductor devices. Using these methods, featureshaving a minimum dimension of less than about 40 nm may be formed.

Turning to the composition of cured polyimide resin layer 130B of FIGS.1A through 1C, cured polyimide resin layer 150 of FIG. 2 and curedpolyimide resin layer 205 of FIGS. 3A through 3C, FIGS. 4A and 4B andFIGS. 5A and 5B, there are three general formulations of uncuredpolyimide resins. It should be understood that for the purposes of thepresent invention curing an oligomer implies cross-linking the oligomerto form a polymer or cross-linked polymer or resin.

The polyimide medium or imaging layer of the embodiments of the presentinvention advantageously meets certain criteria. These criteria includehigh thermal stability to withstand millions of write and erase events,low wear properties (low pickup of material by tips), low abrasion (tipsdo not wear out easily), low viscosity for writing, glassy characterwith little or no secondary relaxations for long data bit lifetime, andshape memory for erasability.

Thermal and oxidative stability was imparted to cured polyimide resinsby incorporating a large aromatic content in the polymer backbone and byladder type linkages such as imide functionalities. Cured polyimideresins according to embodiments of the present invention have hightemperature stability while maintaining a low glass transitiontemperature (T_(g)), which is contrary to current teaching that hightemperature stability results in a high T_(g) and vice versa. In oneexample, cured polyimide resins according to embodiments of the presentinvention are thermally and oxidatively stable to at least 400° C.

Wear and erasability of the media were improved by cross-linking thepolyimide oligomers without increasing the T_(g) which was unexpected.By placing the cross-linking sites at the chain ends, the molecularweight of polyimide oligomers is predefined and therefore cross-linkingwas found to have a lesser effect upon the glass transition temperaturethan is currently thought. The width of the transition from the rubberyto glassy state of the cured polyimide resin was found not to increasesignificantly over that of the polyimide oligomer. The sharp andpractically temperature-invariant transition from the glassy to rubberystate as seen in polyimide oligomers was maintained in the cross-linkedresin. Again, this is contrary to what is currently thought. Themolecular weights of the polyimide oligomers themselves are controlledby the ratio of anhydride, amine and reactive endgroup precursor used inthe polyimide oligomer synthesis.

Further control over the cross-link density was achieved by addingcontrolled amounts of reactant diluents described infra that enhancecross-linking. These reactive diluents formed a high density ofcross-links that enhanced the wear properties of the polyimide mediumwithout greatly increasing the T_(g) or width of the glass transition.

The glass transition temperature was adjusted for good writeperformance. To optimize the efficiency of the write process thereshould be a sharp transition from the glassy state to the rubbery state.A sharp transition allows the cured resin to flow easily when a hot tipis brought into contact and quickly return to the glassy state once thehot tip is removed. However, too high a T_(g) leads to high writecurrents and damage to the probe tip assemblies described supra.Incorporation of flexible aryl ether and thioether linkages resulted inpolyimide resins of lower than expected T_(g). In one example, curedpolyimide resins of the embodiments of the present invention have T_(g)sof less than about 250° C., preferably between about 120° C. and about250° C., more preferably between about 120° C. and 150° C.

Long data bit lifetime of the polyimide resin medium was obtained by theincorporation of hetero-atoms such as oxygen and sulfur in the polyimideresin backbone and varying the catenation of aromatic rings from para tometa linkages.

A first formulation of uncured polyimide resin comprises polyimideoligomers having the structure:

wherein R′ is selected from the group consisting of

wherein R″ is selected from the group consisting of

wherein n is an integer from about 5 to about 50.

The endgroups, having the structure:

provide the cross-linking of the polyimide oligomers into a polyimideresin. The reactive endgroup is the phenylethynyl group of structure(XI). In one example, curing is performed at about 300° C. to about 350°C. In one example, polyimide oligomers according to the firstformulation (and of the second formulation described infra)advantageously have a molecular weight of from about 4,000 Daltons toabout 15,000 Daltons.

In a second formulation of uncured polyimide resin, one or more of thefollowing reactive diluents (including combinations of differentstructures (XII)) is added to the first formulation:

where R₁, R₂ and R₃ are each independently selected from the groupconsisting of hydrogen, alkyl groups, aryl groups, cycloalkyl groups,alkoxy groups, aryloxy groups, alkylamino groups, arylamino groups,alkylarylamino groups, arylthio, alkylthio groups and

It should be noted that reactive diluents XII and XIII contain threesubstituted phenylethynyl groups. The phenylethynyl groups of thepolyimide oligomers and the phenylethynyl groups reactive diluentsprovide the cross-linking of the polyimide oligomers into a polyimideresin. In one example, curing is performed at about 300° C. to about350° C.

In one example, a Tg of a cured polyimide resin layer formed using thesecond formulation of the present invention with a reactive diluent iswithin about 50° C. of a Tg of an otherwise identical cured polyimideresin layer formed without the reactive diluent.

FIG. 6 is a diagram illustrating cross-linking of a polyimide resin witha reactive diluent according to embodiments of the present invention. InFIG. 6, a mixture of straight chain polyimide oligomer 250 of repeatingunits n and having two reactive endgroups 255 (which representsstructure (I)) and a reactive diluent 260 having three reactivefunctionalities 265 (representing structures (XII and XIII) is heatcured to produce a cross-linked polyimide resin 270. In resin 270,polyimide oligomers 250 are linked to each other through respectivereactive endgroups; polyimide oligomers 250 are linked to reactivediluents 260 through respective reactive endgroups and reactive diluents260 and linked to each other through respective reactive endgroups.Although Tg is usually a function of molecular weight and cross-linkdensity, in this case it is largely independent of the percentage byweight of reactive diluent in the polyimide oligomer/reactive diluentmixture.

A third formulation of uncured polyimide resin comprises linearpolyimide oligomers having the structure:

E-R¹+A₁-A₂-A₃- . . . -A_(N)R²-R¹-E;  (XIV)

wherein E is

wherein each of A₁, A₂, A₃ . . . A_(N) is independently selected fromthe group consisting of:

wherein R¹ is selected from the group consisting of

wherein R² is selected from the group consisting of

wherein R³ is

wherein N is an integer greater than or equal to 2;wherein at least one of A₁, A₂, A₃ . . . A_(N) is

wherein at least one of A₁, A₂, A₃ . . . A_(N) is

In one example, polyimide oligomers according to the third formulationadvantageously have a molecular weight of from about 4,000 Daltons toabout 15,000 Daltons. In one example the integer value of N in structure(XIV) is consistent with a molecular weight of from about 4,000 Daltonsto about 15,000 Daltons. In one example, the value of N in structure(XIV) is no greater than about 50.

It should be understood that in structure (XIV) the monomers representedby structures (XVI) and (XVII)) may be arranged in a linear sequencewith (a) all structures (XVI) in one subsequence and all structures(XIV) in another subsequence, (b) in an alternating sequence, (c) inother regular repeating sequences or (d) in random sequence.

EXPERIMENTAL

All materials were purchased from Aldrich and used without furtherpurification unless otherwise noted.

Preparation of Thioether Dianhydride Oligomers (mTEDA and pTEDA)

Either 1,3-benzenedithiol or 1,4-benzenedithiol was dissolved in DMSO(20% solids) with triethylamine and 4-fluorophthalic anhydride. Themixture was heated to 60° C. for 4 hours and then either the mTEDA orpTEDA was precipitated on ice, filtered, and re-crystallized twice fromDMSO/acetic anhydride.

Preparation of Phenylene Ether Dianhydride Oligomers

A bisphenol (e.g. 4-hydroxyphenyl ether) was dissolved in dry DMF with4-nitrophthalonitrile and potassium carbonate. The solution was heatedto 120° C. and the water generated was removed by azeotropicdistillation with toluene. After 24 hours, the solids were precipitatedon ice. The resulting solid was collected by vacuum filtration. Thesolid was then refluxed in toluene, ethanol, and hydrochloric acid tohydrolyze the nitrile groups to carboxylic acids. The mixture was againpoured over ice and the resulting solid collected by vacuum filtration.The tetraacid was then dissolved in toluene and acetic anhydride, andheated to reflux for 8 hours. The resulting precipitate was collected byvacuum filtration and re-crystallized from acetic anhydride.

Preparation of Diamines

A bisphenol was dissolved in dry DMF with 4-fluoronitrobenzene, andpotassium carbonate. The same procedure was followed as above for thenucleophilic aromatic substitution. The resulting solid was dissolved inTHF, and NaBH₄ was added slowly. The reaction was allowed to stirovernight and the product was collected by removal of the solvent undervacuum, and then extracted with CH₂Cl₂ and water. The organic phase wascollected and the solvent removed under vacuum. The resulting solid waspurified by vacuum sublimation.

Preparation of Bishydroxyphenylethers

The reagent 3-bromophenol was reacted with benzylbromide in the presenceof potassium carbonate and 18-crown-6 in THF for 24 h. The reactionmixture was filtered to remove excess potassium carbonate and resultantpotassium bromide, and the solvent was removed under vacuum. Theremaining liquid was filtered through silica to give3-bromophenylbenzylether in 92% yield. This product was then dissolvedin dry NMP together with resorcinol, copper iodide, cesium carbonate,and tetramethylheptanedione. The mixture was stirred vigorously andheated at 120° C. for 72 hours. The solution was then precipitated bypouring over ice and extracted with methylene chloride. The organicphase was collected and the solvent removed. The resulting oil wasdissolved in toluene and concentrated hydrochloric acid and heated toreflux.

Polyimide Oligomer Synthesis from Amic Acid

In a dry atmosphere, the oligomers, a diamine, and acetic anhydride weredissolved in dry cyclohexanone (20% solids) and allowed to stir for 24hours. The poly(amic acid) formed was used to cast films fromcyclohexanone. NMR spectra of the amic acids were acquired by removal ofthe solvent under vacuum and the addition of dry DMSO-d₈.

Polyimide Oligomer Synthesis by Chemical Imidization

Under an inert atmosphere, a bisanhydride and a diamine (purified byvacuum sublimation) were dissolved in dry NMP and allowed to stir for 24hours. Acetic anhydride and triethylamine were then added and thereaction was allowed to stir under inert atmosphere for 48 hours.Finally the mixture was heated to 60° C. for 2 hours and thenprecipitated by pouring into stirring methanol. The resulting solid waswashed on the frit with water, and methanol, and re-precipitated twicefrom cyclohexanone (or NMP).

Film Preparation from Polyimide

The polymer was dissolved in cyclohexanone (5% by weight) and filteredthrough a 0.2-micrometer filter onto UV/ozone cleaned silicone wafers.The wafer was then spun at 2500 rpm for 30 seconds yielding anapproximately 100 nm thick film. The films were cross-linked on ahotplate under an inert atmosphere with a heating program of a 1-hourramp from 50° C. to 350° C. and held an additional hour at 350° C. Bulkfilms and samples containing reactive diluent structure (XIII) wereprepared in a similar fashion except for bulk films where a 20 weight %solution was used.

Film Preparation from Amic Acid

Under dry atmosphere, the polyamic acid precursors were diluted withcyclohexanone to the appropriate concentration (5% solids). Minimizingthe exposure to ambient air, films of the precursor were spun at 2500rpm for 30 seconds and then cured with a heating program of a 1-hourramp from 50° C. to 350° C. and held an additional hour at 350° C.

In a first synthesis example, polyimide resins of varying molecularweights were synthesized by varying the ratios of the two oligomers1,3-bis(4-aminophenoxy)benzene (XXVIII) and4,4′(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (XXIX) and theend capping agent 4-phenylethynylpthalic anhydride (XXX). Bulk samplesand thin films of these materials were prepared and then cured at 350°C. for one hour to yield highly cross-linked films.

One preparation (Sample A) of structure (XXXI) was extensively studied.In structure (XXXI), the integer value of n is consistent with amolecular weight of about 14,400 Daltons. Cured sample A had a <Mn>14,400 g/mol, Mw/Mn=1.9 and when cured at 350° C. had a Tg of about 175°C. In structure (XXXI), the integer value of n is consistent with amolecular weight of about 14,400 Daltons.

In a second synthesis example:

It should be understood that in structure (XXXIII) the first monomerwhich is enclosed by ( )_(n) and the second monomer which is enclosed by( )_(m) should not be construed as limiting structure (XXXIII) to anyparticular sequence of first and second monomers. Structure (XXXIII)includes structures where the first and second monomers may be arrangedin a linear sequence (a) with all first monomers in one subsequence andall second monomers in another subsequence, (b) in an alternatingsequence, (c) in other regular repeating sequences or (d) in randomsequence.

Other Syntheses

In order to reduce the glass transition temperature, the rigidity of thepolymer backbone must be decreased. To that end, polyimide oligomerswith an increased number of flexible aryl ether linkages as well asthioether linkages were synthesized.

Dianhydride phenylene ether containing oligomers was synthesized fromthe reaction of 4-nitrophthalonitrile with the requisite bisphenolprecursor followed by hydrolysis of the cyano groups and dehydration toform the cyclic anhydride. The thioether variants were synthesizeddirectly in one step from the reaction of a bisthiophenol with4-fluorophthalic anhydride. This synthetic scheme allowed a series ofether- and thioether-containing oligomers with two or more ether orthioether linkages and all possible combinations of meta and paracatenation. Furthermore the scheme was easily adapted to synthesize anumber of phenylene ethers containing diamines with the same variationon number of ether linkages and catenation schemes by reaction of abisphenol derivative with 4-fluoronitrobenzene and subsequent reductionof the nitro group to an amine.

The thioether dianhydrides were reacted with a series of diamines and4-phenylethynylphthalic anhydride in specific ratios to yield polyimideoligomers with molecular weights ranging from 4×10³ g/mol to 10×10³g/mol. The first step in the polymerization mechanism is the reaction ofone diamine with one anhydride to form an amic acid. One of two stepscan be taken at this point. For polymers where the fully imidized formexhibited good solubility and good film forming properties withcyclohexanone as the solvent, the polymer was imidized by a chemicaldehydration with triethyl amine and acetic anhydride, and then isolatedand characterized. With certain polymer compositions, the fully imidizedmaterial was difficult to process. To circumvent these issues withsolubility and film forming properties, these polymers were processedinto thin films from the amic acid. The polymers were then imidizedthermally as thin films concurrently with the final cross-linkingreaction. The amic acid precursors were analyzed by removal of thesolvent under vacuum and transferred to dry sample containers with driedand distilled solvents for analysis by GPC and ¹H-NMR. The thermal andmechanical properties of cured films were studied by TGA, DSC, and DMA.

Example of synthesis and structures of thioether containing dianhydrideoligomers:

TABLE 1 Properties of thioether based polyimides

or

<M_(n)> × T_(g) before T_(g) cured Dianhydride Diamine 10⁻³ g/mol cure °C. ° C. pTEDA APTE 4.0 T_(m) 261(a) 162 mTEDA APTE 4.0 163 178 mTEDAmAPB 7.0 (b) (b) mTEDA mAPB 7.0 (c) 209 Processed from amic acid mTEDAmAPB 14.0 (c) 151 Processed from amic acid where

(a) T_(m) indicates the temperature at which the sample melted. (b)Semicrystalline, Tg not available. (c) In processing from amic acid,cross-linking occurs concurrently with the conversion of the acid to thepolyimide. Therefore there is no opportunity to measure Tg previous tocross-linking.

Example Synthesis of bis-4,4′-isophthaloyloxyphenylene ether.

The phenylene ether materials exhibited similar solubility limitationsas the thioether based materials. However, when all linkages in thediamine and the dianhydride were meta catenated, materials showed muchimproved solubility in solvents such as THF and cyclohexanone. Thesematerials could be processed either from the amic acid or fully imidizedstates. Exclusively para catenated materials also exhibitedsemi-crystalline properties. However, once cured, the films were nolonger crystalline due to the cross-links preventing crystallization ofthe chains. Working from the amic acid precursors avoided all solubilityissues associated with the para-arylene ether polymers.

TABLE 2 Phenylene ether based polyimides, imidized chemically % II % III<M_(n)> × 10⁻³ g/mol T_(g) before cure ° C. T_(g) cured ° C. 100 0 10.0T_(m) 261 162 50 50 10.0 163 178where

and the integer value of n is consistent with a molecular weight ofabout 10,000 Daltons.

FIG. 7 is thermo-gravimetric analysis (TGA) plotting percentage ofweight remaining and temperature versus time of a polyimide resinaccording to an embodiment of the present invention compared topolystyrene resins. The primary limiting factor in the use ofpolystyrene (PS) or of polystyrene-co-vinylbenzocyclobutene (PSBCB) fora storage medium was poor thermal stability. The results of a TGA studyshowed that polyimides resins outperformed PS and PSBCB resins. Thestyrenic material began to decompose rapidly once the furnace reached250° C. while the polyimide resin showed no appreciable degradationuntil above 350° C. in scanning TGA and no weight loss over hours at250° C. in isothermal TGA. The polyimide resin used in this TGA studywas (XXXI).

FIG. 8 is a plot of modulus versus temperature polyimide resinsaccording to embodiments of the present invention. FIG. 8 plots thestorage modulus versus temperature for cured sample A and for apolyimide resin made by curing sample A with 30% by weight reactivediluent structure (XIII). Cured sample A exhibited a change in modulusof about 3 decades transitioning from the glassy state to the rubberystate. Cured sample A and 30% by weight reactive diluent structure(XIII) exhibited a drop in modulus of about 2 decades transitioning fromthe glassy state to the rubbery state. The Tg range for both samples wasabout the same with a Tg of about 175° C. In general a polyimide resinlayer according to embodiments of the present invention had a modulusabove a glass transition temperature between about 1.5 and about 3.0decades lower than a modulus of the polyimide resin layer below theglass transition temperature of the polyimide resin layer.

FIGS. 9A through 9D are SEM photomicrographs of tips of various tipassemblies. FIG. 9A is an SEM photomicrograph of an unused tip 120 (seeFIG. 1A). FIG. 9B is an SEM photomicrograph of a worn tip 120 after useon a polystyrene layer.

FIG. 9C is an SEM photomicrograph of an worn tip 120 after use on aPSBCB layer showing pickup of the storage medium. FIG. 9D is an SEMphotomicrograph of tip 120 after about 2.4E6 write/erase and about 2.3E8read cycles of a polyimide resin medium according to embodiments of thepresent invention. As can be seen there is virtually no tip wear.

FIG. 10 is an AFM scan-line cross-section showing data bits written in astorage medium according to an embodiment of the present invention. InFIG. 10 a pattern of data bits (indentation for a “1”, no indentationfor a “0”) were written and the definition of the data determined usingan AFM. Each “1” bit generated a very sharp and distinct signal, whilethe noise generated by “0” bits was very low. The write pitch was 34 nmwhich is greater than 500 Gb/inch².

Thus, the embodiments of the present invention provide data storage andimaging methodologies that operate in the nanometer regime.

The description of the embodiments of the present invention is givenabove for the understanding of the present invention. It will beunderstood that the invention is not limited to the particularembodiments described herein, but is capable of various modifications,rearrangements and substitutions as will now become apparent to thoseskilled in the art without departing from the scope of the invention.Therefore, it is intended that the following claims cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

1. A method, comprising: heating a probe to at least 100° C.; pushingsaid heated probe into a cross-linked resin layer of polyimideoligomers; and removing said probe from said resin layer, resulting information of a deformed region in said resin layer.
 2. The method ofclaim 1, wherein said polyimide oligomers have the structure:

wherein R′ is selected from the group consisting of

wherein R″ is selected from the group consisting of

wherein n is an integer from about 5 to about
 50. 3. The method of claim2, wherein said layer of polyimide oligomers includes a reactivediluent, said reactive diluent selected from the group consisting of:

where R₁, R₂ and R₃ are each independently selected from the groupconsisting of hydrogen, alkyl groups, aryl groups, cycloalkyl groups,alkoxy groups, aryloxy groups, alkylamino groups, arylamino groups,alkylarylamino groups, arylthio, alkylthio groups and

wherein said polyimide oligomers are cross-linked by reactive diluentgroups derived from said reactive diluent during said curing.
 4. Themethod of claim 3, wherein a glass transition temperature of said resinlayer with said reactive diluent groups is within about 50° C. of aglass transition temperature of an otherwise identical resin layerformed without said reactive diluent groups.
 5. The method of claim 1:wherein said polyimide oligomers have the structure:E-R¹A₁-A₂-A₃- . . . -A_(N)R²-R¹-E; wherein E is

wherein each of A₁, A₂, A₃ . . . A_(N) is independently selected fromthe group consisting of:

wherein R¹ is selected from the group consisting of

wherein R² is selected from the group consisting of

wherein R³ is

wherein N is an integer greater than or equal to 2; wherein at least oneof A₁, A₂, A₃ . . . A_(N) is

wherein at least one of A₁, A₂, A₃ . . . A_(N) is


6. The method of claim 1, wherein after said curing, said resin layer iscross-linked by said reactive endgroups of said polyimide oligomers. 7.The method of claim 1, wherein said polyimide oligomers include reactivependent groups attached along backbones of said polyimide oligomers andafter said curing, said resin layer is cross-linked by said reactivependent groups.
 8. The method of claim 1, wherein a glass transitiontemperature of said resin layer is less than about 250° C.
 9. The methodof claim 1, wherein a modulus of said resin layer above a glasstransition temperature of said resin layer is between about 1.5 andabout 3.0 decades lower than a modulus of said resin layer below saidglass transition temperature of said resin layer.
 10. The method ofclaim 1, wherein said resin layer is thermally and oxidatively stable toat least 400° C.
 11. The method of claim 1, further including: removingsaid resin layer in said deformed region to form an exposed region of asubstrate and a region of substrate protected by said resin layer; andmodifying at least a portion of said exposed region of substrate. 12.The method of claim 1, further including: dragging said probe in adirection parallel to a top surface of said resin layer while heatingand pushing said probe, resulting in formation of a trough in said resinlayer.
 13. The method of claim 1, wherein said cross-linked resin layerhas a thickness between about 10 nm and about 500 nm and a thicknessvariation of less than about 1.0 nm across said cross-linked resinlayer.
 14. A method, comprising: bringing a thermal-mechanical probeinto proximity with a resin layer multiple times to induce deformedregions at points in said resin layer, said resin layer comprisingcross-linked polyimide oligomers, said thermal mechanical probe heatingsaid points in said resin layer above about 100° C. and thereby writinginformation in said resin layer.
 15. The method of claim 14, furtherincluding: bringing a thermal-mechanical probe into proximity with saidpoints to read said information.
 16. The method of claim 15, furtherincluding: bringing a thermal-mechanical probe into proximity with oneor more of said deformed regions in said resin layer, said thermalmechanical point heating said one or more of said deformed regions toabove about 100° C., thereby deforming said one or more of said deformedregions in such a way as to eliminate said one or more deformed regions,thereby erasing said information.
 17. The method of claim 16, furtherincluding: repeatedly writing, reading and erasing information at pointsin said resin layer.
 18. The method of claim 14, wherein said polyimideoligomers have the structure:

wherein R′ is selected from the group consisting of

wherein R″ is selected from the group consisting of

wherein n is an integer from about 5 to about
 50. 19. The method ofclaim 18, said resin layer further including reactive diluent groups,said polyimide oligomers cross-linked by said reactive diluent groups,said reactive diluent groups derived from reactive diluents selectedfrom the group consisting of:

where R₁, R₂ and R₃ are each independently selected from the groupconsisting of hydrogen, alkyl groups, aryl groups, cycloalkyl groups,alkoxy groups, aryloxy groups, alkylamino groups, arylamino groups,alkylarylamino groups, arylthio, alkylthio groups and


20. The method of claim 19, wherein a glass transition temperature ofsaid resin layer with said reactive diluent groups is within about 50°C. of a glass transition temperature of an otherwise identical resinlayer formed without said reactive diluent.
 21. The method of claim 14,wherein said polyimide oligomers have the structure:E-R¹A₁-A₂-A₃- . . . -A_(N)R²-R¹-E; wherein E is

wherein each of A₁, A₂, A₃ . . . A_(N) is independently selected fromthe group consisting of:

wherein R¹ is selected from the group consisting of

wherein R² is selected from the group consisting of

wherein R³ is

wherein N is an integer greater than or equal to 2; wherein at least oneof A₁, A₂, A₃ . . . A_(N) is

wherein at least one of A₁, A₂, A₃ . . . A_(N) is


22. The method of claim 14, wherein said resin layer is cross-linked bysaid reactive endgroups of said polyimide oligomers.
 23. The method ofclaim 14, wherein said polyimide oligomers include reactive pendentgroups attached along backbones of said polyimide oligomers and aftersaid curing, said resin layer is cross-linked by said reactive pendentgroups.
 24. The method of claim 14, wherein a glass transitiontemperature of said resin layer is between about 120° C. and about 250°C.
 25. The method of claim 14, wherein a modulus of said resin layerabove a glass transition temperature of said resin layer is betweenabout 1.5 and about 3.0 decades lower than a modulus of said resin layerbelow said glass transition temperature of said resin layer.
 26. Themethod of claim 14, wherein said cross-linked resin layer has athickness between about 10 nm and about 500 nm and a thickness variationof less than about 1.0 nm across a writeable region of said cross-linkedresin layer.
 27. A data storage device, comprising: a recording mediumcomprising a resin layer overlying a substrate, in which topographicalstates of said resin layer represent data, said resin layer comprisingcross-linked polyimide oligomers; and a read-write head having one ormore thermo-mechanical probes, each of said thermo-mechanical probesincluding a resistive region locally heating a tip of saidthermo-mechanical probe in response to electrical current being appliedto said thermo-mechanical probe; and a scanning system for scanning saidread-write head across a surface of said recording medium.
 28. The datastorage device of claim 27, wherein said polyimide oligomers have thestructure:

wherein R′ is selected from the group consisting of

wherein R″ is selected from the group consisting of

wherein n is an integer from about 5 to about
 50. 29. The data storagedevice of claim 28, said resin layer further including reactive diluentgroups, said polyimide oligomers cross-linked by said reactive diluentgroups, said reactive diluent groups derived from reactive diluentsselected from the group consisting of:

where R₁, R₂ and R₃ are each independently selected from the groupconsisting of hydrogen, alkyl groups, aryl groups, cycloalkyl groups,alkoxy groups, aryloxy groups, alkylamino groups, arylamino groups,alkylarylamino groups, arylthio, alkylthio groups and


30. The data storage device of claim 29, wherein a glass transitiontemperature of said resin layer with said reactive diluent groups iswithin about 50° C. of a glass transition temperature of an otherwiseidentical resin layer formed without said reactive diluent.
 31. The datastorage device of claim 27, wherein said polyimide oligomers have thestructureE-R¹A₁-A₂-A₃- . . . -A_(N)R²-R¹-E; wherein E is

wherein each of A₁, A₂, A₃ . . . A_(N) is independently selected fromthe group consisting of:

wherein R¹ is selected from the group consisting of

wherein R² is selected from the group consisting of

wherein R³ is

wherein N is an integer greater than or equal to 2; wherein at least oneof A₁, A₂, A₃ . . . A_(N) is

wherein at least one of A₁, A₂, A₃ . . . A_(N) is


32. The data storage device of claim 27, wherein said resin layer iscross-linked by said reactive endgroups of said polyimide oligomers. 33.The data storage device of claim 27, wherein said polyimide oligomersinclude reactive pendent groups attached along backbones of saidpolyimide oligomers and after said curing, said resin layer iscross-linked by said reactive pendent groups.
 34. The data storagedevice of claim 27, wherein a glass transition temperature of said resinlayer is between about 120° C. and about 250° C.
 35. The data storagedevice of claim 27, wherein a modulus of said resin layer above a glasstransition temperature of said resin layer is between about 1.5 andabout 3.0 decades lower than a modulus of said resin layer below saidglass transition temperature of said resin layer.
 36. The data storagedevice of claim 27, comprising: wherein said one or morethermal-mechanical probes are arranged in a two dimensional array; and aheat control circuit for independently applying said electrical currentto each of same one or more thermo-mechanical probes; a write controlcircuit and for independently controlling heating of each of said one ormore thermo-mechanical probes by said heat control circuit to write databits to said recording medium; an erase control circuit forindependently controlling heating of each of said one or morethermo-mechanical probes by said heat control circuit to erase data bitsfrom said recording medium; and a read control circuit for independentlyreading data bits from said recording medium with each of said one ormore thermo-mechanical probe.
 37. The data storage device of claim 27,further including: a contact mechanism for contacting said recordingmedium with respective tips of said one or more thermo-mechanicalprobes.
 38. The data storage device of claim 27, wherein saidcross-linked resin layer has a thickness between about 10 nm and about500 nm and a thickness variation of less than about 1.0 nm across awriteable region of said cross-linked resin layer.